I don’t want to go to work tomorrow 😭 is this normal for a part time position?

I’m a part time employee. Its my first job so sorry if I sound stupid. But full time at my work is 40 hours a week. I think that is standard? Well, as I said, I’m part time. But I was scheduled for 45 hours this week. I’m tired and I have no time for my school work. I take an online college course that requires a lot of essays. So I don’t have much time to write it. I don’t know what to do. Is this normal? I feel like I’m being taken advantage of. I’m only part time for a reason. It’s because I don’t want 40 hours a week. But since I get paid less, I feel like they use me for the cheaper labor. It’s the holiday season so it’s busier. But I feel like that isn’t my problem and they should hire more people and not let other employees use their vacation time during this time. I’m just upset and stressed. I can’t talk to my boss because the schedule is already set and done. There’s no way of fixing it for this week and they’d have no one else to schedule anyhow. Just wondering if this is normal and if I’m justified in feeling stressed.